http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48760
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot
com> 2011-04-25 16:02:11 UTC ---
On Mon, 25 Apr 2011, paolo.carlini at oracle dot com wrote:
> A C snippet showing the issue would be:
>
> int main()
> {
> float r = 0;
> float i = __builtin_nanf ("");
>
> __complex__ float c = r + i * 1.0fi;
>
> /*
> __complex__ float c;
> __real__ c = r;
> __imag__ c = i;
> */
>
> __builtin_printf("%f\n", __real__ c);
> __builtin_printf("%f\n", __imag__ c);
> }
>
> Indeed, I could tweak the library to construct the complex by pieces, avoiding
> the multiplication by the imaginary constant in the constructor, but the
> problem would definitely reappear at any following multiplication...
I don't see any C bug here. Without imaginary types it's correct that
1.0fi is a complex constant and so you get NaN for both real and imaginary
parts. To avoid that, assign to real and imaginary parts as shown in the
comment, or implement __builtin_cmplx* that correspond to C1X CMPLX*
macros (which should be pretty easy to do; the built-in functions just
need to map to COMPLEX_EXPR and handle constants correctly) and use those.
